How critical is the exact placement of the tonearm

Less than 0.5mm is about right. You have some room to compensate by changing overhang via moving the cartridge back or forth.

Good luck!!

Dear Headsnappin: The Restock answer resume ( in some ways ) the importance about. You could be not dead precise on the tonearm mounting if you are precise in the cartridge set-up specialy and very specific in the overhang distance.

Regards and enjoy the music.
Raul.

It's hard for me to believe anyone could drill a hole that large in an armboard and get it within .01969 of an inch.... Then get the armboard mounted that precisely... I'm not saying it's not critical, just the nature of the drill bit that size.

I don't believe anyone said the hole had to have that tolerance. There is play within the hole to adjust the arm to that tolerance which can be achieved with micrometers and other measuring tools. The actual drilled hole would have a much greater tolerance. Then again you would be surprised how accurate a drill press can be - let alone plowing it out with a Bridgeport if you wanted to get ridiculous.

Zen,
I design circuit boards. I deal with .001 inch every minute of every day. I have 3 points. 1) one wouldn't want that much "slop" in the hole size. Just tightening the arm would cause it to move more than that. 2) I'd bet you be surprised at how much runout the typical homeowners drill press has 3) at that size, the typical drill bit has a pretty large tolerance.

IMHO, to get the hole that precisely located and sized, one would have to use a CNC controlled drill and a very expensive, high tolerance bit.

Not to mention the fact that you are, usually, dealing with a fiberous material such as wood, or worse yet, mdf.

Just my 2 cents.